1. Field of the Invention
The present invention relates to a water base ink for ink-jet recording.
2. Description of the Related Art
In the ink-jet printing system, ink droplets are formed by the ink discharge system including, for example, the electrostatic attraction system, the system in which mechanical vibration or displacement is applied to the ink by using a piezoelectric element or the like, and the system in which bubbles are generated by heating the ink to utilize the pressure generated thereby. All or a part of the ink droplets are adhered to a recording objective material such as paper to perform the printing.
As the ink used for such an ink-jet recording system, a water base ink is used in which various kinds of dyes or pigments are dissolved or dispersed in a liquid medium composed of water or composed of water and water-soluble organic solvent.
In the ink-jet recording system, in order to obtain a recorded image which is satisfactory for a long period of time, there are demands such as (1) the physical property values of the ink (viscosity, surface tension, and density) are appropriate values; (2) neither any appearance of deposit due to the heat occurs or any change in the physical property values is caused, so that the clog-up in a nozzle or orifice of the recording apparatus is prevented and the discharge stability is obtained; and (3) the recorded image is excellent in water resistance and light resistance or the like. In addition, it is demanded that (4) the nozzle diameter of a recording head of an ink-jet printer is decreased to make a minute ink droplet discharged from the nozzle in order to realize satisfactory printing property showing no blurring of the ink even on a regular paper without using an exclusive ink-jet paper.
However, when the nozzle diameter of the recording head is decreased, there is the following problem. Namely, when an ink-jet printer is left to stand for a long period of time with an ink cartridge attached thereto, foreign matters are generated in, or enter into, a nozzle of the head or a narrow ink channel inside the head, which in turn prevents an ink from smoothly passing through the nozzle of the head or the ink channel, thereby causing a discharge failure. This problem most likely occurs to Color Index Number (C.I.) Direct Yellow 132 used as the coloring agent in the ink. C. I. Direct Yellow 132 is preferred dye for the yellow ink because it is excellent in the color vividness and brightness.
In order to solve the problem, it has been proposed to add a large amount of a humectant so as to prevent the deposition of dye due to the evaporation of water or low temperatures, or to use benzotriazole so as to suppress the change in the physical properties of the ink (U.S. Pat. No. 5,560,771 corresponding to Japanese Patent No. 3089665).
Example A of U.S. Pat. No. 5,560,771 discloses a yellow ink in which C.I. Direct Yellow 132 is used as the dye and which contains diethylene glycol. However, this ink is different from the ink of the present invention in composition and components.
However, in a conventional water base ink for ink-jet recording, the method of adding a large amount of humectant involves inconveniences in which the viscosity of the ink is increased and thus any optimal viscosity cannot be obtained. In addition, there is the following problem. The surroundings of a nozzle of an ink head is be dried more quickly under the hot and dry environment. When the dye is deposited from the ink attached to the surrounding of nozzle, it is hard to remove the deposited dye. In particular, this problem is serious in the high-temperature areas. Although the ink-jet printer of recent model is provided with a wiper for wiping the surface of the head, once the dye is deposited and solidified, it cannot be removed with the wiper. In addition, during transportation of an ink cartridge, for example, by air, or in use of the ink cartridge in a cold region, the ink is exposed to a low-temperature environment and thus the dye may be deposited. With the conventional method, it is difficult to simultaneously prevent the deposition of dye after the evaporation of water and the deposition of dye at low temperatures. Namely, there is a problem that even when it is possible to prevent the deposition of the dye after the evaporation of water, it is difficult to prevent the deposition of the dye under the low temperatures. Or, on the contrary, even when it is possible to suppress the deposition of the dye under the low temperatures, it is difficult to prevent the deposition of the dye after the evaporation of water. In particular, in the inks using C.I. Direct Yellow 132 as the dye, the foregoing problem has not been solved as far as the inventors are aware of.
The present invention has been made in order to solve the above problems, an object of which is to provide a water base ink for ink-jet recording using C.I. Direct Yellow 132 in which any foreign matters such as deposition of dye does not occur and the stability in long-term storage is obtained.